Neurophysiological activity underlying altered brain metabolism in epileptic encephalopathies with CSWS

We investigated the neurophysiological correlate of altered regional cerebral glucose metabolism observed in children with epileptic encephalopathy with continuous spike-waves during sleep (CSWS) by using a multimodal approach combining time-sensitive magnetic source imaging (MSI) and positron emission tomography with [(18)F]-fluorodeoxyglucose (FDG-PET). Six patients (4 boys and 2 girls, age range: 4-8 years, 3 patients with Landau-Kleffner syndrome (LKS), 3 patients with atypical rolandic epilepsy (ARE)) were investigated by FDG-PET and MSI at the acute phase of CSWS. In all patients, the onset(s) of spike-waves discharges were associated with significant focal hypermetabolism. The propagation of epileptic discharges to other brain areas was associated with focal hypermetabolism (five patients), hypometabolism (one patient) or the absence of any significant metabolic change (one patient). Interestingly, most of the hypometabolic areas were not involved in the epileptic network per se. This study shows that focal hypermetabolism observed at the acute phase of CSWS are related to the onset or propagation sites of spike-wave discharges. Spike-wave discharges propagation can be associated to other types of metabolic changes, suggesting the occurrence of various neurophysiological mechanisms at the cellular level. Most of the hypometabolic areas are not involved in the epileptic network as such and are probably related to a mechanism of remote inhibition. These findings highlight the critical value of combining FDG-PET with time-sensitive functional neuroimaging approaches such as MSI to assess CSWS epileptic network when surgery is considered as a therapeutic approach.